The invention relates to a device in an electrophotographic copier having a light source with a given spectral distribution for extinguishing a recorded electrostatic charge image.
Electrophotographic copiers are known wherein an electrostatic charge image is produced in a layer consisting of a photoconductive material such as arsenic-selenium. In these copiers, the layer is charged with the aid of a corona discharge. The erasure of a recorded charge image is normally carried out with the light of a spectral range producing maximum photoconductivity. In the case of arsenic-selenium (As.sub.2 Se.sub.3), which has been given by way of example, this spectral range lies in the green light zone at approximately 500 nm. The recording of the charge image is generally carried out using light from the same spectral range. However, proposals have also already been made such as for example in the earlier patent application U.S. Ser. No. 821,133 filed Aug. 21, 1977 of which I am co-inventor, for recording using light from the red spectral range. These proposals enable the recording of an electrostatic charge image which is not eliminated, but regenerated by the conventional corona charge. The erasure of a charge image recorded in this way is carried out in the conventional manner using green light as given above. Details of these proposals may be gathered from the above noted application which is incorporated herein by reference.
It has been proven that in electrophotographic copies of the described type, in the case of at least a number of photoconductive materials such as used for the aforementioned layer, fatigue effects occur. These fatigue effects occur in particular in the case of photoconductors having a mobility distribution which is dependent upon field strength, including the aforementioned As.sub.2 Se.sub.3. A fatigue effect of this kind is described for example in German Offenlegungsschrift No. P 20 37 456.
The fatigue effect described in the aforementioned Offenlegungsschrift may be eliminated, as described therein, by carrying out a modified illumination of the photoconductive layer, the modification being dependent upon the actually existing surface potential of the photoconductor.
The fatigue phenomenon becomes manifest due to the fact that in the case of multiple, successive, cyclic charging of the photoconductive layer by corona discharge, a continuous decrease in the surface potential actually achieved occurs. This leads to contrast changes in the copies when the copier is used continuously.
The device described in the German Offenlegungsschrift No. P 20 37 456 at the least presents difficulties in maintaining the charging potential, and consequently for maintaining the constrast potential for recording light from copy to copy.